CN100377567C - FM and AM mixed net point net shape controlling method in multi-position imaging depth device - Google Patents

FM and AM mixed net point net shape controlling method in multi-position imaging depth device Download PDF

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CN100377567C
CN100377567C CNB2005101166363A CN200510116636A CN100377567C CN 100377567 C CN100377567 C CN 100377567C CN B2005101166363 A CNB2005101166363 A CN B2005101166363A CN 200510116636 A CN200510116636 A CN 200510116636A CN 100377567 C CN100377567 C CN 100377567C
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output
value
point
pixel
net
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CN1767586A (en
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李海峰
杨斌
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Peking University
Beijing Founder Electronics Co Ltd
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Peking University
Beijing Founder Electronics Co Ltd
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Priority to EP06722425A priority patent/EP1942656A4/en
Priority to PCT/CN2006/000857 priority patent/WO2007048290A1/en
Priority to JP2008536907A priority patent/JP4499176B2/en
Priority to US12/091,287 priority patent/US8045233B2/en
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40Picture signal circuits
    • H04N1/405Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4055Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern
    • H04N1/4057Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern the pattern being a mixture of differently sized sub-patterns, e.g. spots having only a few different diameters
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40Picture signal circuits
    • H04N1/405Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4051Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size
    • H04N1/4052Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
    • H04N1/4053Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions with threshold modulated relative to input image data or vice versa

Abstract

The present invention relates to a frequency modulation and amplitude modulation mixed net point net shape controlling method on a multi-position imaging depth device. In the prior art, the reproduction of net shapes on different hierarchy tones is completely based on an error random diffusion theory and is influenced by an output mechanism of the dynamic control of multi-position net points, and the controllability of the net point shapes on a certain hierarchy tone is difficult to guarantee. The method induces a dynamic statistical algorithm of the output gray scale of adjacent directions on the basis of the prior art to guarantee the controllability of the net point shapes and solve the randomness of net shape change brought by the randomness of error diffusion. The adoption of the method provided by the present invention can give full play to the characteristics of the multi-position imaging device on the basis of the existing multi-position frequency modulation and amplitude modulation mixed net hanging method according to the requirements of the imaging of the device to net points, and the method can output the frequency modulation and amplitude modulation half tone mixed net hanging effect of the net points of which the shape change is controlled under low resolution, solve the problem of granular sensation when the mixed half tone net points are actually output, and guarantee the smooth effect of the hierarchy tones.

Description

Frequency modulation and amplitude modulation mixed net point net shape control method on multi-position imaging depth equipment
Technical Field
The invention belongs to a halftone dot generation method in the field of image hard copy reproduction, and particularly relates to a frequency modulation and amplitude modulation mixed dot network type control method on a multi-bit imaging depth device.
Background
The hard copy reproduction of images mainly relates to the screen plate making technology of printers and high-grade printing plate making equipment. Screening techniques for hard copy reproduction of images are also known as digital image halftoning techniques. Digital image halftoning techniques can be divided into two categories, amplitude modulated screening and frequency modulated screening. Amplitude modulation screening is also called gathering point ordered dithering technology, and is characterized by that the dyeing points of the produced halftone image are adjacently gathered together in pairs on the geometric position so as to form a cluster of dyeing regions, these dyeing regions are also called halftone dots, and because the gathering point ordered dithering technology adopts the method of controlling halftone dot area to reproduce grey scale of original image, so that it is called amplitude modulation halftone dot.
In the prior art, based on the technology of mixed networking of frequency modulation network and amplitude modulation network, there is a Chinese patent application "a method of error diffusion frequency modulation networking based on double feedback" (application number: 200510068127.8, published 2005, 9/14). The frequency modulation and amplitude modulation mixed halftone dot technology in the technical scheme disclosed by the patent application is mainly based on a halftone dot generation general algorithm on the basis of one-bit or multi-bit imaging depth equipment, and when halftone dots are output by actual equipment, because the screen type reappearance of the halftone dots on different levels of tones in the prior art is completely based on an error random diffusion theory, the controllability of halftone dot shapes at a certain level of tones cannot be ensured. Meanwhile, the multi-bit depth imaging equipment is influenced by a multi-bit dot dynamic control output mechanism, the multi-bit dots are more difficult to operate on the network type controllability, and finally, the shape and the characteristics of the output multi-bit dots do not completely have the characteristics of the hierarchical increasing uniformity of the dots and the like of the multi-bit dots, and the output of the actual equipment mainly shows that the sizes of the dots are not consistent, and the quality problems of unsmooth granular feeling and the like of the whole image caused by the inconsistent sizes of the dots and the like affect the image output quality.
For the frequency modulation and amplitude modulation halftone mixing halftone dots output by the multi-bit imaging depth equipment, because the halftone mixing halftone dots have the characteristic of the halftone dot size of amplitude modulation halftone dots, the variation of the halftone dot size on different levels is similar to that of amplitude modulation halftone dots, the halftone dot size is continuously increased along with the improvement of the levels, and the halftone dots in a low-density area are independently varied and separated from each other; in the intermediate density area, the mesh points gradually start to be mutually overlapped and connected along with the increase of the size of the mesh points, so that the independent mesh points and the mutually overlapped mesh points coexist in the density area. Based on the influence of randomness on the dot characteristics of the two density areas, the dot shape characteristics are different, and a series of problems of unsmooth dot output quality are caused, so that the main contradiction on the requirement of solving the quality problem of the multi-bit mixed dots lies in how to solve the problem of the control method on the dot shape coordination of the low-density area and the medium-density area.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a frequency modulation and amplitude modulation mixed mesh point network type control method on a multi-position imaging depth device. The method not only can ensure that the original frequency modulation and amplitude modulation multi-position mixed dot technology has controllability of the dot shape, but also can solve the randomness of the change of the net shape caused by the randomness of error diffusion, thereby effectively playing the output effect of the mixed halftone mixed dot of the multi-position imaging depth equipment on the printing of the high-quality imaging equipment and improving the output quality of the mixed dot.
In order to achieve the above purposes, the invention adopts the technical scheme that: a frequency modulation and amplitude modulation mixed mesh point net type control method on a multi-bit imaging depth device comprises the following steps:
the method comprises the following steps: firstly, dividing the hierarchical tone range of 0 to 255 into 2 according to the image bit depth n of the device n 1 different region:
[0,R 1 ],(R 1 ,R 2 ],...,(R i-1 ,R i ],...(R 2n-2 ,255]
the corresponding bit output lattice ranges are as follows:
(0,Out 1 ),(Out 1 ,Out 2 ),...,(Out i-1 ,Out i ),...(Out 2n-2 ,11...1)
wherein: out 1 Is n bit depth binary representation;
taking the threshold M of the middle point in each region i As a threshold comparison parameter for the region;
step two: at [0, 255]Within the hierarchy tone range of (2), setting an n-bit imaging depth output probability threshold value L i
Further, at [0, 255]Within the range of gradation level of (2) n 2 integers as n-bit imaging depth output probability threshold: l is 1 ,L 2 ,...,L i ,...L 2n-2 The size of the probability threshold is adjustable, and the probability threshold can be correspondingly changed according to the output requirement of actual equipment so as to achieve the optimal output quality;
step three: in 2 n -1 distinct regions (R) i-1 ,R i ]In the method, the frequency modulation and amplitude modulation mixed network hanging method based on error diffusion double feedback respectively carries out corresponding operation processing, and the specific processing method comprises the following steps:
(1) Firstly, scanning and inputting a manuscript image, carrying out threshold value comparison operation T on final input pixels g' (m, T) of the manuscript image, and converting the operation result into corresponding pixels b (m, T) of a halftone image;
furthermore, when scanning and inputting the original image, a bidirectional scanning method is adopted, that is, for each line of the continuously scanned original, scanning is performed from left to right for one line first, scanning for the next line is performed from right to left, and the scanning is performed in an interlaced manner until all lines are scanned completely.
(2) Comparing the result pixel b (m, t) with the input pixel g '(m, t)) to which the threshold value is determined, and calculating an error value e (m, t) which is a difference between the result pixel b (m, t) and the input pixel g' (m, t);
(3) Performing multiplication operation on the error value e (m, t) and a preset weight distribution value through an error diffusion filter e, and then diffusing the error value e (m, t) to unprocessed pixels around the current processing pixel, and adding and summing the original document pixel value g (m, t) at the diffused position and the error value diffused to the pixel to obtain a new original document pixel input value g' (m, t);
further, the error diffusion filter e here adopts the diffusion principle and the weight distribution coefficient of the following table:
** d 5 d 3
d 2 d 4 d 5 d 4 d 2
d 1 d 2 d 3 d 2 d 1
wherein, represents the pixel position of the current point, the arithmetic ratio of other positions represents the diffusion weight value at the position opposite to the current pixel, the value range is [0,1], and satisfies:
2×d 1 +4×d 2 +2×d 3 +2×d 4 +2×d 5 ∈[0,1]。
(4) In parallel with the operations of the steps (2) and (3), performing product operation on the currently processed pixel output value b (m, t) and a diffusion filter w, performing dithering processing, diffusing the dithered pixel output value to surrounding corresponding unprocessed pixels, accumulating the dithered pixel output value and the parameters of error diffusion in the two steps, and performing final addition and summation on the dithered pixel output value b (m, t) and the original input pixel output value g (m, t) to obtain a final input pixel value g' (m, t);
further, here, the diffusion direction of the diffusion filter w is set as follows:
** w 0
w 3 w 2 w 1
wherein: the scanning direction from left to right represents the position of the current point pixel, the parameters of other positions represent the diffusion weight values at the position corresponding to the current pixel, the value range is [0,1], and the following conditions are satisfied:
w 0 +w 1 +w 2 +w 3 ∈[0,1]。
further, the dithering algorithm for the diffusion filter w is processed as follows:
fRand=(R(m,t)/R_MAX-0.5)×cDither
dw 0 =w 0 -fRand
dw 2 =w 2 +fRand
dw 1 =w 1 +fRand
dw 3 =w 3 -fRand
in the above formula: fRand is a jitter fine tuning parameter; r (m, t) is a random value-taking parameter of the current point of scanning; RMAX is the maximum value of the random parameter R (i); cDither is a jitter amplitude adjusting parameter which determines the quality of the amplitude modulation characteristic; dw 0 ~dw 3 For diffusion filtering after ditheringThe weight spread values in different directions of w.
(5) Looping through steps 1) through 4) above until all input pixels g (m, t) are processed.
Step four: in the region (R) i-1 ,R i ) While realizing the mixed net hanging, according to the probability threshold value L i And the net-shaped control accumulated value Shapecur of the current point, combining the original dynamic variable hierarchical output mechanism and adopting an adjacent direction output gray dynamic statistical calculation method:
the dynamic variable level output method comprises the following calculation formula:
generate a pseudo-random value for the current point from Shapecur:
F i = random (Shapecur), equation 1
Wherein: the pseudorandom function random can be automatically generated in the context of compilation F i ∈[0,255];
And (3) dynamically calculating and outputting dot matrix data:
Figure C20051011663600091
equation 2
The specific steps of outputting the gray scale dynamic calculation output lattice data control network type in the adjacent direction are as follows:
(1) Determining a net type control adjustment density area according to the stability and the output linearization characteristics of the multi-bit imaging depth equipment;
(2) Determining the shape of the mesh points to be adjusted according to the requirements of pulse width adjustment technical parameters of the multi-bit imaging depth equipment and the requirements of the existing random mesh types in different density areas and the equipment output stability on the mesh point shapes in different density areas;
(3) Determining the shape of the target mesh point and the shape of the mesh point which should be avoided according to the mesh point shape which is determined in the step (2) and needs to be adjusted by combining the imaging characteristics of the output equipment;
(4) Finally, according to the dot density area and the existing output gray level, adopting an adjacent direction output gray dynamic statistical algorithm to determine the output range parameter of the multi-bit mixed halftone binary dot, wherein the control point setting method in the algorithm comprises the following steps:
1) Setting an output gray value a of a point before the current point, wherein the output gray value of the point before a is b;
2) Setting the gray value of a point at the current point position in a row before the current point as c, the gray value of the point before c is d, and the gray value of the point after c is e;
3) Setting the gray value of the point at the same position in the previous row with the output gray value c as f;
4) Setting output gray scale statistical parameters around the current point:
Sum 1 =a+c+d Sum 2 =a+b Sum 3 =c+f
wherein, sum 1 Representing the sum of the gray levels of a 2X2 rectangular area around the current point,
Sum 2 representing the sum of the first two output grays in the horizontal direction of the current point,
Sum 3 indicating the summation of the first two output grays in the vertical direction of the current point.
And further, in the fourth step, two methods for dynamically controlling the output gray value are simultaneously adopted. The two methods for dynamically controlling the output gray value respectively comprise the following steps: a dynamic variable level output method, a dynamic statistical method of output gray scale in adjacent direction. The two methods are not available.
The invention has the following effects: the method provided by the invention can give full play to the characteristics of the multi-position imaging equipment according to the requirements of equipment imaging on the mesh points on the basis of the original error diffusion double-feedback multi-position frequency modulation and amplitude modulation mixed mesh hanging method, can output the frequency modulation and amplitude modulation halftone mixed mesh hanging effect with controllable mesh point shape change under low resolution, solves the granular sensation problem of the mixed halftone mesh points during actual output, and ensures the smooth effect of the gradation.
Drawings
FIG. 1 is a schematic diagram of the dynamic statistics of adjacent output gray levels
FIG. 2 is a schematic view of the dot shape of the low density region before adjustment
FIG. 3 is a schematic view of the dot shape of the medium density region before adjustment
FIG. 4 is a schematic view of the adjusted low density region dot shapes
FIG. 5 is a schematic view of the adjusted intermediate density region dot shape
FIG. 6 is a comparison graph of dot output effect
Detailed Description
The invention is further described below with reference to the following figures and examples:
the invention discloses a frequency modulation and amplitude modulation mixed net hanging method based on the existing error diffusion double-feedback multi-bit imaging depth, which adopts a net point shape dynamic accurate control generation algorithm to realize a frequency modulation and amplitude modulation mixed net point net type control method on multi-bit imaging depth equipment, and the specific implementation mode is as follows:
in this embodiment, the imaging depth of the output device is set to two bits, that is, n =2, and the existing pulse width adjustment technology of the device has the following requirements on the mesh points: (setting pure white to 255 and pure black to 0)
In the low-density regions (171 to 255): since the dots are not overlapped and are independent of each other, the dot output value of a single pixel is required to be 3 (binary 11), the dot output combination of two pixels is the combination of 3 and 1, and the horizontal or longitudinal arrangement of 3 and 3 cannot exist in the dot combination of three pixels or more.
In the medium density region (84-171): because the independent dots and the overlapped dots exist at the same time, except for the requirement of a low-density area, the output of the dots is closer to the characteristic of 2-bit imaging depth dots by following the principle of most consistency of the same level of the sizes of the dots and the principle of increasing of the pixel arrangement level of the dots.
In the high density region (0 to 84): since the output device in the example is a low-resolution laser printer, the requirement of the density area for printing linear features is not limited, and the density area is still output according to the original output principle of the multi-bit dots.
According to the above requirements of the output device, the concrete practical solution is as follows:
the method comprises the following steps: firstly, according to the image bit depth n =2 of the device, the hierarchy scale range of 0 to 255 is equally divided into 2 n -1=3 distinct zones:
[0,84],(84,171],(171,255]
the corresponding bit output lattice ranges are as follows:
(11,10),(10,01),(01,00)
wherein: in this embodiment, when actually outputting, the pure black is set to 0, and the pure white is set to 255.
Taking the threshold M of the middle point in each region i As a threshold comparison parameter for the region, then:
M 1 =42 M 2 =127 M 3 =212
step two: at [0, 255]Within the range of gradation level of (2) n -2=2 integers as n-bit imaging depth output probability threshold: l is a radical of an alcohol 1 =8,L 2 =24, the output probability of 11, 10, 01, 00 is controlled through the threshold probability, and thus the output effect of 2-bit mixed dots is achieved;
step three: in the above 3 different areas, the existing fm-am hybrid network hanging method based on error diffusion dual feedback is respectively processed by corresponding operations, and the specific processing method is as follows:
(1) Firstly, scanning and inputting an original image, performing threshold value comparison operation T on pixels g' (m, T) of the original image, and converting the operation result into corresponding pixels b (m, T) of a halftone image;
here, in order to avoid the interference phenomenon caused by the scanning direction and the randomly distributed dot frequency when scanning the pixel data of the original document, it is commonly called "network collision", and in this embodiment, a bidirectional scanning method is adopted.
(2) Comparing the resultant pixel b (m, t) with the input pixel g' (m, t)) for which the domain value is found, and calculating an error value e (m, t) which is a difference between the two;
(3) The error value e (m, t) is multiplied by a certain weight distribution value through a diffusion filter e and then diffused to unprocessed pixels around the current processing pixel, and the original document pixel value g (m, t) at the diffused position is added with the error value diffused to the pixel to obtain a new original document pixel input value g' (m, t). The error diffusion filter adopts the diffusion principle and the weight distribution coefficient of the following table:
** d 5 d 3
d 2 d 4 d 5 d 4 d 2
d 1 d 2 d 3 d 2 d 1
wherein, represents the pixel position of the current point, and the arithmetic ratio of other positions represents the diffusion weight value at the position opposite to the current pixel, in this embodiment, the following parameters are adopted:
d 1 =1/44 d 2 =2/44 d 3 =5/44 d 4 =4/44 d 5 =8/44
the above steps 2 and 3 complete the first diffusion feedback operation, and realize the basic principle of error diffusion.
(4) In parallel with the operations of the steps (2) and (3), the currently processed pixel output value b (m, t) and the second diffusion filter w are subjected to product operation, dithering processing is carried out, the pixel output value b (m, t) is diffused to the corresponding surrounding unprocessed pixels, the pixel output value b (m, t) and the pixel output value are accumulated with the parameters of error diffusion in the two steps, and then the pixel output value b (m, t) and the original input pixel g (m, t) are subjected to final addition and summation to serve as a final input pixel value g' (m, t). The diffusion direction of the second filter w is here set as follows:
** w 0
w 3 w 2 w 1
wherein: the scanning direction is from left to right, wherein x represents the position of the current point pixel, the parameters of other positions represent the diffusion weight values at the position corresponding to the current pixel, the value range is [0,1], and the following conditions are satisfied:
w sum =(w 0 +w 1 +w 2 +w 3 )∈[0,1]。
the dithering algorithm in this embodiment is processed by the following algorithm:
fRand=(R(m,t)/R_MAX-0.5)×cDither
dw 0 =w 0 -fRand
dw 2 =w 2 +fRand
dw 1 =w 1 +fRand
dw 3 =w 3 -fRand
in the above formula: fRand is a jitter fine tuning parameter; r (m, t) is a random value of the current point of scanningA parameter; r _ MAX is the maximum value of the random parameter R (i); cDither is a jitter amplitude adjusting parameter which determines the quality of the amplitude modulation characteristic; dw 0 ~dw 3 The values are diffused for the weights in different directions of the post-dither filter w.
And (5) finishing the second diffusion feedback operation in the step (4), and realizing the amplitude modulation characteristic of the frequency modulation network.
In the present embodiment, the above parameters are set as follows:
w 0 =w 2 =0.175, w 1 =w 3 =0.025, then w sum =0.4
cDither=0.2
In the process of hanging the net, w is adjusted sum Changing the size of the frequency-modulated dots by w 0 ~w 3 And (5) distributing values to adjust the shape of the frequency modulation dots.
(5) And (4) circulating the steps (1) to (4) until all the input pixels g (m, t) are processed.
Step four: realizing mixed net hanging in 3 equal areas and simultaneously according to probability threshold value L 1 =8, L 2 =24 and the current point net control cumulative value ShapeCur, dynamic variable hierarchical output mechanism, the algorithm is as follows:
the pseudo-random value for the current point is generated according to ShapeCur in conjunction with equation 1:
F=random(ShapeCur),
wherein: the pseudo-random function random may be automatically generated in a compilation environment. F is an element [0, 255]
And (4) dynamically calculating and outputting the lattice data according to the formula 2.
The control network type of the output lattice data by dynamically calculating the output gray scale in the adjacent direction is realized as follows:
1) Determining a mesh-type control adjustment density area according to the stability of the multi-bit imaging depth device and the output linearization characteristics.
The adjusted density region determined in this example is: low density regions (171-255) and medium density regions (84-171).
2) Determining the shape of the mesh points to be adjusted according to the pulse width adjustment technical parameter requirement of the multi-bit imaging depth equipment and by combining the existing random mesh types in different density areas and the requirement of the equipment output stability on the mesh point shapes in the different density areas;
in this embodiment, the dot shapes of the low density regions (171-255) to be adjusted can be referred to in fig. 2, and the dot shapes of the medium density regions (84-171) to be adjusted can be referred to in fig. 3.
3) Determining the shape of the target screen point and the screen point shape which should be avoided according to the screen point shape which is determined in the step 2) and needs to be adjusted by combining the imaging characteristic of the output equipment.
In this embodiment, the shape of the target dots in the low density region is shown in fig. 4, where a symbol denotes an output gray level to be adjusted, and the value is 1 or 0; the medium density region target dot shape is shown in fig. 5. In fig. 4 and 5, ideally, the central gray scale value of the 2-bit halftone dot is 3.
4) Finally, according to the dot density area and the existing output gray level, the output gray level dynamic statistical algorithm in the adjacent direction is adopted to determine the output range parameter of the multi-bit mixed halftone binary dot. According to the target determined in the second step and the third step, the embodiment adopts the following pseudo code to realize the steps:
in the dynamic statistical algorithm of the output gray scale according to the adjacent direction, the method for setting the control point is as follows:
1) Setting the output gray value a of the previous point of the current point, wherein the output gray value of the previous point is b;
2) Setting the gray value of a point at the current point position in a row before the current point as c, the gray value of the point before c is d, and the gray value of the point after c is e;
3) Setting the gray value of the point at the same position in the previous row with the output gray value c as f.
4) Setting statistical parameters of output gray levels around the current point:
Sum 1 =a+c+d Sum 2 =a+b Sum 3 =c+f
the above a, b, c, d, e, f ∈ [0,3] (in the example, the two-bit halftone dot has 4 output levels), and the detailed distribution diagram is shown in fig. 1 (the dynamic statistical diagram of adjacent output grayscales).
The logic for realizing the two-bit net point statistical pseudo code is as follows:
IF (input pixel value ∈ [ 84-171 ]) middle density area
{
IF(Sum 1 ==9)
Binary range of output Gray values [10, 01]
ELSE IF (a! =0& & c! =0& & d! =0& & input pixel value ∈ [123, 171 ])
Binary range of output Gray values [00, 00]
ELSE IF(Sum 3 >=5)&&Input pixel value e [123, 171])
Binary range of output Gray values [00, 00]
ELSE IF(Sum 1 <3&&Input pixel value e [139, 171])
Binary range of output Gray values [11, 00]
ELSE IF(Sum 2 ==6&&Input pixel value e [123, 171])
Binary range of output Gray values [00, 00]
ELSE IF(Sum 1 >=7&&Input pixel value e 139, 171])
Binary range of output Gray values [00, 00]
ELSE
Output according to a' dynamically variable hierarchy mechanism
}
IF (input pixel value ∈ (171, 255)) low density region
{
IF(a==3||c==3)
{
IF((a==3 && c==3)||
(a==3 && (c!=3&&c!=0))||
(a!=3 && a!=0)&&c==3))
Binary range of output Gray values [00, 00]
ELSE
Binary range of output Gray values [01, 00]
}
ELSE IF(((a!=3 && a!=0) &&(c!=3 && c!=0))||
(c!=3 && c!=0 && d==0 && e==0)||
a!=3 && a!=0 && b==3)
Binary range of output Gray values [00, 00]
ELSE
Binary range of output Gray values [11, 00]
}
Based on the 2-bit depth imaging depth device, in combination with the steps of the above embodiments, 2-bit tone amplitude modulation hybrid screening can be implemented, and a screening effect map thereof is compared with the original 2-bit hybrid screen dots, as shown in fig. 6, where the map in the first row is a screen dot sample before modification, and the map in the second row is a modified sample.
The method of the present invention is not limited to the embodiments described in the specific embodiments, and other embodiments can be derived by those skilled in the art according to the technical solutions of the present invention, and the method also belongs to the technical innovation scope of the present invention.

Claims (10)

1. A frequency modulation and amplitude modulation mixed dot net type control method on a multi-bit imaging depth device comprises the following steps:
the method comprises the following steps: firstly, dividing the hierarchical tone range of 0 to 255 into 2 equally according to the image bit depth n of the equipment n -1 different region:
[0,R 1 ],(R 1 ,R 2 ],...,(R i-1 ,R i ],...(R 2n-2 ,255]
the corresponding bit output lattice ranges are as follows:
(0,Out 1 ),(Out 1 ,Out 2 ),...,(Out i-1 ,Out i ),...(Out 2n-2 ,11...1)
wherein: out i Is n bit depth binary representation;
taking a threshold M of the middle point in each region i As a threshold comparison parameter for the region;
step two: at [0, 255]Within the range of the gradation, an n-bit imaging depth output probability threshold value L is set i
Step three: in 2 n -1 distinct regions (R) i-1 ,R i ) In the method, the frequency modulation and amplitude modulation mixed net hanging method based on error diffusion double feedback is respectively carried out corresponding operation processing;
step four: in the region (R) i-1 ,R i ) While realizing the mixed net hanging, according to the probability threshold value L i And the network type control accumulated value Shapecur of the current point, and the network type change is controlled by dynamically calculating and outputting the lattice data by combining the original dynamic variable hierarchical output mechanism and adopting a dynamic statistical algorithm of outputting the gray scale in the adjacent direction.
2. A fm am hybrid halftone image processing method for multi-bit imaging depth devices as set forth in claim 1, wherein: in the second step, setting 2 n 2 integers as n-bit imaging depth output probability threshold: l is a radical of an alcohol 1 ,L 2 ,...,L i ,...,L 2n-2 And correspondingly adjusting the size of the probability threshold according to the output requirement of the actual equipment.
3. A fm-am hybrid halftone dot pattern control method on a multi-bit imaging depth device as defined in claim 1, wherein: the concrete method for dynamically calculating and outputting the lattice data to control the network type change in the step four comprises the following steps:
(1) Determining a net type control adjustment density area according to the stability and the output linearization characteristics of the multi-bit imaging depth equipment;
(2) Determining the shape of the mesh point to be adjusted according to the requirements of the pulse width adjustment technical parameters of the multi-bit imaging depth equipment and the requirements of the existing random mesh types in different density areas and the equipment output stability on the mesh point shapes in the different density areas;
(3) Determining the shape of a target mesh point and the shape of the mesh point which should be avoided according to the mesh point shape which is determined in the step (2) and needs to be adjusted by combining the imaging characteristic of the output equipment;
(4) Finally, according to the dot density area and the existing output gray level, a dynamic statistical algorithm of the output gray levels in the adjacent directions is adopted to set control points around the current point, so that the output range parameters of the multi-bit mixed halftone binary dot are determined.
4. A fm/am hybrid halftone dot pattern control method for a multi-bit imaging depth device as defined in claim 3, wherein: the method for setting the control points around the current point in the dynamic statistical method for outputting the gray scales in the adjacent directions adopted in the step (4) comprises the following steps:
1) Setting the output gray value a of the previous point of the current point, wherein the output gray value of the previous point is b;
2) Setting the gray value of a point at the current point position in a line before the current point as c, the gray value of the point before the current point as d, and the gray value of the point after the current point as e;
3) Setting the gray value of the point at the same position in the previous row with the output gray value c as f;
4) Setting output gray scale statistical parameters around the current point:
Sum 1 =a+c+d Sum 2 =a+b Sum 3 =c+f
wherein, sum 1 Representing the 2x2 rectangular area around the current point plus the sum of the gray levels,
Sum 2 representing the sum of the first two output grays in the horizontal direction of the current point,
Sum 3 indicating the summation of the first two output grays in the vertical direction of the current point.
5. A method of fm-am hybrid halftone image processing on a multi-bit imaging depth device as claimed in claim 1, 2,3 or 4, wherein: in the fourth step, the adopted dynamic variable hierarchical output mechanism dynamically calculates and outputs the lattice data, and the algorithm is as follows:
generate a pseudo-random value for the current point from Shapecur:
F i = random (Shapecur), equation 1
Wherein: the pseudorandom function random can be automatically generated in the context of compilation F i ∈[0,255];
And (3) dynamically calculating and outputting dot matrix data:
equation 2.
6. A fm/am hybrid halftone dot pattern control method on a multi-bit imaging depth device as claimed in claim 5, wherein: in the fourth step, the following two methods for dynamically controlling the output gray value are simultaneously adopted: a dynamic variable hierarchical output method and an adjacent direction output gray dynamic statistical method.
7. A fm-am hybrid halftone dot pattern control method on a multi-bit imaging depth device as defined in claim 1, wherein: in the third step, the corresponding processing comprises a frequency modulation and amplitude modulation hybrid network hanging method based on error diffusion double feedback, which comprises the following steps:
(1) Firstly, scanning and inputting a manuscript image, performing threshold value comparison operation T on final input pixels g' (m, T) of the manuscript image, and converting the operation result into corresponding pixels b (m, T) of a halftone image;
(2) Comparing the result pixel b (m, t) with the input pixel g '(m, t)) to which the threshold value is calculated, and calculating an error value e (m, t) which is a difference between the result pixel b (m, t) and the input pixel g' (m, t);
(3) The error value e (m, t) is multiplied by a preset weight distribution value through an error diffusion filter e and then diffused to unprocessed pixels around the current processing pixel, and the original document pixel value g (m, t) at the diffused position and the error value diffused to the pixel are added and summed to obtain a new original document pixel input value g (m, t);
(4) In parallel with the operations of the steps (2) and (3), performing product operation on the currently processed pixel output value b (m, t) and a diffusion filter w, performing dithering processing, diffusing the dithered pixel output value to surrounding corresponding unprocessed pixels, accumulating the dithered pixel output value and the parameters of error diffusion in the two steps, and finally adding and summing the dithered pixel output value b (m, t) and the original input pixel output value g (m, t) to obtain a final input pixel value g' (m, t);
(5) The above (1) to (4) are looped until all the input pixels g (m, t) are processed.
8. A method of fm-am hybrid halftone image processing on a multi-bit imaging depth device as claimed in claim 7, wherein: in the step (1), a bidirectional scanning method is adopted when scanning the original image, namely, for each line of the continuously scanned original, scanning is performed from left to right, then scanning of the next line is performed from right to left, and the scanning is performed in an interlaced manner in the same way until all lines are scanned completely.
9. A method of fm-am hybrid halftone image processing on a multi-bit imaging depth device as claimed in claim 7 or 8, wherein: and (3) adopting the diffusion principle and the weight distribution direction of the following table by the error diffusion filter e:
** d 5 d 3
d 2 d 4 d 5 d 4 d 2
d 1 d 2 d 3 d 2 d 1
wherein, represents the pixel position of the current point, the arithmetic ratio of other positions represents the diffusion weight value at the position corresponding to the current pixel, the value range is [0,1], and satisfies:
2×d 1 +4×d 2 +2×d 3 +2×d 4 +2×d 5 ∈[0,1]。
10. a method of fm-am hybrid halftone image processing on a multi-bit imaging depth device as claimed in claim 9, wherein: the diffusion direction of the diffusion filter w in the step (4) is set as follows:
** w 0
w 3 w 2 w 1
wherein: the scanning direction from left to right represents the position of the current point pixel, the parameters at other positions represent the diffusion weight values at the positions corresponding to the current pixel, the value range is [0,1], and the following conditions are satisfied:
w 0 +w 1 +w 2 +w 3 ∈[0,1];
in the step (4), the dithering algorithm of the diffusion filter w is processed by adopting the following method:
fRand=(R(m,t)/R_MAX-0.5)×cDither
dw 0 =w 0 -fRand
dw 2 =w 2 +fRand
dw 1 =w 1 +fRand
dw 3 =w 3 -fRand
in the above formula: fRand is a jitter fine tuning parameter; r (m, t) is a random value-taking parameter of a current scanning point; r _ MAX is the maximum value of the random parameter R (i); cDither is the jitter amplitude adjustment parameter, dw 0 ~dw 3 Are the weighted diffusion values in different directions of the post-dither diffusion filter w.
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